WebGL 2 is an extension to WebGL 1. The WebGL2RenderingContext interface implements all members of the WebGLRenderingContext interface. Some methods of the WebGL 1 context can accept additional values when used in a WebGL 2 context. You will find this info noted on the WebGL 1 reference pages.

The WebGL tutorial has more information, examples, and resources on how to get started with WebGL.